EDITORS: Downloadable images are available at http://www.engin.umich.edu/news/imagebank/

ANN ARBOR—A team of engineering students from the University of Michigan has designed and built an entire satellite for an upcoming NASA mission.

Weighing in at only 50 pounds and about the size of a small microwave oven, the box-like satellite is named Icarus after the Greek legend of the man who flew too close to the sun, melted his wax-covered wings, and plunged into the Aegean sea. If everything goes right, the painstakingly hand-built satellite will meet a similar fate, burning up in the Earth’s atmosphere a week or two after its mission begins sometime in the fall 2000.

Though student teams at Michigan have flown experiment packages on the space shuttle and participated in building sub-systems of satellites before, the Icarus project will be the first entirely student-built U-M satellite to be flown by NASA.

“It was made to function as an autonomous satellite,” said student project manager Jane Ohlweiler, a master’s degree student in space systems engineering—or satellite-making. The package’s primary function is to act as a weight to pull a 9-mile-long string called a tether out from a spool on a spent Delta II rocket booster. If everything works as designed, Icarus will end up sailing along at the end of this tether like an orbital plumb bob. “First and foremost, we’re a dead weight at the end of the tether,” Ohlweiler acknowledges.

But rather than making the box a mere lump of mass, the students have covered Icarus with solar cells and crammed it full of instruments that will gather data on the tether’s motion and position and then beam that information down to listening stations around the Earth. The finished satellite will be a rectangular box about 18 inches long and a foot high, and all of it—the aluminum box, the instruments inside it, the complex network of wiring, and even the circuit boards that make it work—were designed, built and tested entirely by the student team.

“Our mission is to prove that we can do this,” said B.T. Cesul, a senior in chemical engineering and assistant manager of the project. “And we’re helping NASA prove the smaller, faster, cheaper model.”

Icarus is part of a larger mission in which Brian Gilchrist, associate professor of electrical engineering and computer science and associate professor of atmospheric, oceanic and space sciences, is participating called ProSEDS, the Propulsive Small Expendable Deployer System. The primary mission of the Delta II rocket launch will be to lift a Global Positioning System satellite into orbit sometime this fall. Once that is done, ProSEDS will get to work. Icarus, the spool of tether, and an array of instruments to gauge the experiment’s success will be mounted on the side of the rocket’s second-stage booster.

Normally, a spent booster like this would take as much as a year and a half to tumble into reentry and burn up, but ProSEDS aims to bring it down in 21 days or less. Gilchrist and his colleagues who have been studying varying uses for space tethers think the fuel-free source of thrust created by a 15-kilometer kite string could be a boon to satellite operators. Though nobody anticipated this problem in the go-go years of the 1960s and 1970s, space has become a fairly hazardous place to fly, with thousands of bits of dead spacecraft and spare parts zinging around. A cost-effective way to quickly deorbit spent payloads, pull big things like space stations into higher orbit, or even to do mundane tasks like taking out a space station’s trash, would be a great improvement. For example, if tethers were used to help keep the new International Space Station aloft for 10 years, the savings over conventional fuels would be about $2 billion, NASA estimates.

As the ProSEDS project took shape, it was Gilchrist’s idea to hand over the entire “endmass” project to students. “It’s small enough in scale that students can really handle everything,” Gilchrist said. Icarus started as a class project in
Icarus also represents the latest in a new trend in engineering education being pursued at Michigan—student team projects. Tackling authentic engineering problems and working in an interdisciplinary team helps prepare students for the way engineering is currently being practiced in the real world. “It’s the kind of thing you don’t learn in the classroom,” said Ohlweiler, sitting shoulder to shoulder with her teammates in a cramped office plastered with posters from U.S. and Russian space missions. Nearly 100 students from six different engineering disciplines have been involved. “We’ve had everybody from freshmen to Ph.D.s participating and doing things they never thought they’d get a chance to do,” Ohlweiler said.

NASA’s move toward smaller, cheaper missions also opens up a world of new learning experiences for students interested in learning about space systems design, said Lennard Fisk, chair of U-M Department of Atmospheric, Oceanic and Space Sciences. “It used to be that rockets were the only option for hardware training, but this new generation of small satellites opens up all kinds of opportunities.”

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HOW IT WORKS

At 250 miles of altitude, the drag created by the tether isn’t from air resistance, it’s from the Earth’s magnetic field. The first 5 kilometers of the tether are a conductive wire that captures passing electrons and sends them streaming toward the Delta II rocket booster. The interaction between that electrical current and the Earth’s magnetosphere results in a sort of drag that slows the rocket stage down and makes it start to fall. The tether also generates about 100 watts of electricity that can recharge the experiment’s batteries and keep its instruments running. Icarus is powered by some space-grade C batteries and solar panels.

WHY USE TETHERS?

Tether propulsion should work near any planet with a magnetic field, including Jupiter. And it wouldn’t be just for taking things down. This fuel-free source of thrust could also be used to lift satellites and space stations into a higher orbit. One proposal envisions a fleet of tether-powered tug boats in space that would lift satellites up to higher orbits after they’ve been carried aloft by rockets. That’s what NASA terms a “low- recurring-cost space asset” or a good deal.

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EDITORS: For further information, contact Prof. Brian Gilchrist, (734) 763-6230, gilchrst@umich.edu; U-M Icarus Project Office, (734) 936-0511, icarus-m@umich.edu;

http://www.engin.umich.edu/news/imagebank/engineeringchemical engineeringBrian GilchristLennard Fiskgilchrst@umich.edu